In general, a polarizing sheet or polarizing film functions to convert natural light into polarized light. Such polarizing function may be realized with a material with which a polarizing sheet is dyed. A liquid crystal display generally uses an iodine type polarizing film dyed with iodine, as a polarizing material.
Such an iodine type polarizing film is manufactured by dyeing a polyvinyl alcohol (PVA) film with dichroic iodine or dichroic dyes and orienting the PVA film in a predetermined direction by a method such as uniaxial drawing (or orientation) and is widely used in LCDs. For instance, a process including uniaxially orienting an un-oriented PVA film in an aqueous solution and then dipping the oriented PVA film in a solution containing iodine and/or potassium iodide, a process including dipping an un-oriented PVA film in a solution containing iodine and/or potassium iodide and then uniaxially orienting the PVA film, a process of uniaxially orienting an un-oriented PVA film in a solution containing iodine and/or potassium iodide, a process including uniaxially orienting an un-oriented PVA film in a dried state and then dipping the oriented PVA film in a solution containing iodine and/or potassium iodide, and the like, may be used to prepare a polarizing film.
The PVA film having iodine adsorbed and oriented therein may be subjected to post-treatment through washing with water or drying to obtain a polarizing film and a polarizing sheet is obtained by laminating a protective film to at least one side of the formed polarizing film.
Meanwhile, in the case where the PVA film is changed (replaced) during manufacture of the polarizing sheet, a sample is taken by preparing a polarizing film through trial operation and then cutting the polarizing film, and a color value of the sample is measured. Thereafter, in order to comply with standard specifications, the sample is generally treated by applying process factors, adding subsidiary materials thereto, and/or diluting the sample.
However, the method of measuring a color value of a polarizing film after preparing the same through trial operation as described above entails problems of increased PVA film loss and production cost due to shut-down of a production line in order to measure the color values. Furthermore, considering that the polarizing film is commonly prepared through a continuous process, consumption of a large amount of PVA film cannot be avoided during measurement of color values.
Accordingly, there is a strong demand for a novel apparatus for controlling a color of a polarizing film capable of solving problems of the conventional art described above and minimizing loss of materials when a PVA film is replaced.